Ni-fe-ta alloys for magnetic recording-reproducing heads

ABSTRACT

A heat-treated ferromagnetic alloy for magnetic recordingreproducing heads, essentially consisting of 60.2 to 85.0 Wt. percent of nickel, 6.0 to 30.0 Wt. percent of iron, and 3.1 to 23.0 Wt. percent of tantalum, and having a Vickers hardness of above 150, a degree of order of 0.1 to 0.6, an electric resistivity of 23 to 94 Mu Omega -cm, initial permeability above 3,000 and maximum permeability above 10,000.

United States Patent [1 1 Masumoto et a].

[ Jan. 15, 1974 NI-FE-TA ALLOYS FOR MAGNETIC RECORDING-REPRODUCING HEADS [75] Inventors: Hakaru Masumoto, Sendai; Yuetsu Murakami, lzumi-machi; Masakatsu Hinai, Natori, all of Japan [73] Assignee: The Foundation: The Research Institute of Electric and Magnetic Alloys [22] Filed: Aug. 23, 1971 [21] App]. No.: 173,964

[30] Foreign Application Priority Data Sept. 17, 1970 Japan 45-80903 [52] [1.8. CI l48/3l.55, 75/170, 148/120, 148/121 [51] Int. Cl C04b 35/00 [58] Field of Search 148/31.55, 121,120; 75/170 [56] References Cited UNITED STATES PATENTS 1,910,309 5/1933 Smith et a1 l48/31.55

2,921,850 l/1960 lnouye et al. 75/170 3,620,719 11/1971 Wheaton 75/170 2,046,995 7/1936 Austin 75/170 1,873,155 8/1932 Scharnow l48/31.55 3,390,443 7/1968 Gould et al. 148/31.55

Primary Examiner-L. Dewayne Rutledge Assistant Examiner-W. R. Satterfield Attorney-Young & Thompson [57] ABSTRACT 4 Claims, 11 Drawing Figures PAIENTEDJAN 1 s w 3. 785.880

' v saw our 10 FIQ'IA INITIAL PERMEABILITY,UO 0F Ni-Fe-To ALLQYS PMENIEM I 3.785.880

SHEET UZUF 10 Fig-l8 MAXIMU ERMEABILITY ;Um 0F Ni-Fe- ALLOYS PATENTED 51974 ,3. 785.880

' SHEET DMIF 1O FIQ'ZB bb' SECTIONS OF FIGS. IA AND lB PAIENIEDJAN I SIGMA I SHEET 06 OF 1.0

xIO 3 O q g 2- ::-l I m 35 ALLOY No.35 ..5 53''. v

I I I 0 5 .l0 l5 HEATING TIME (HOUR) INITIAL PERMEABILITY VS.

HEATING TEMPERATURE v HEATING TIME HOUR) n' -sa MAXIMUM PERMEABILITY VS. HEATING TEMPERATURE AND TIME PA IIII I 51924 sum 07 0F 10 COOLING SPEED C /HOUR) FIQ'4A INITIAL PERMEABILITY v FROM 600C S COOLING SPEED PATENTEUJANISW 3.785.880

SHEET 080F 10 &

5 20 t 2 l5 m 4 l0 l0 :0 IO

COOLING SPEED (C/HOUR MAXIMUM PERMEABILITY VS. COOLING SPEED FROM 600C PATENTED 1 sum user 10 0 mmw w N 0 mm. vfi qr? 5 Y m m -w v O f z 4 .3 2 .l Onw 8v Ewzwa xnd 2523:

MAGNETIC FIELD (0e) PAIENTEDJAH 1. mm

. SHEET 100! 10 AEQ J 3:35am. 258 5 0 O D 5 O5 2 l r I 10 2 I I I15 W l I m 1 5 1 z I O 0 m, m 1 63205: $5 03 TQ(/o) Fig-6 HARDNESS AND RESISTIVITY 0F Cu 73% Ni- Fe-Tu ALLOYS NI-FE-TA ALLOYS FOR MAGNETIC RECORDING-REPRODUCING HEADS BACKGROUND OF THE INVENTION This invention relates to a high-permeability alloy for magnetic recording-reproducing heads, which alloy consists of 60.2 to 85.0 Wt. percent of nickel, 6.0 to 30.0 Wt. percent of iron, 3.1 to 23.0 Wt. percent of tantalum, and an inevitable amount of impurities. With the alloy of the present invention, a high permeability, a high hardness, and a high electric resistivity can be obtained through simple heat treatment, and the alloy can easily be formed into magnetic recordingreproducing heads.

Permalloy (nickel-iron alloy) is widely used at the present in magnetic recording-reproducing heads of audio tape recorder, because it has a;high workability. The conventional Permalloy, however, has a shortcoming in that its Vickers hardness l-Iv is in the order of about 130 and comparatively low, so that its abrasion resistivity is rather poor. Accordingly, there has been a pressing need for improving the hardness and abrasion resistivity of alloy materials for magnetic recording-reproducing heads.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to meet the aforesaid need by providing an alloy having excellent hardness and abrasion resistivity, along with a high permeability.

To achieve the object of the invention, the applicants have carried out a series of tests on alloys, which have a permeability higher than that of binary Permalloy and high hardness and electric resistivity, while maintaining a high workability. As a result, the applicants have found out that, with the addition of 3.1 to 23.0 Wt. percent of tantalum into nickel-iron alloys, magnetic and mechanical properties of the alloy can noticeably be improved.

According to the present invention, there is provided an alloy consisting of 60.2 to 85.0 Wt. percent of nickel, 6.0 to 30.0 Wt. percent of iron, 3.1 to 23.0 Wt. percent of tantalum, and an inevitable amount of impurities, which alloy has a high initial permeability, e.g., 3,000 or higher, a high maximum permeability, e.g., 10,000 or higher, a Vickers hardness greater than 150, and a high electric resistivity. The alloy of the invention can easily be heat treated and formed into the shape of magnetic heads, recording or reproducing. The heat treatment, according to the present invention for providing the desired high permeability'and high hardness, comprises steps of heating the alloy in vacuo or in a non-oxidizing atmosphere, for the purpose of thorough solution treatment and homogenization, at 800 C or higher, preferably 1,100 C or higher, for at least 1 minute, preferably longer than about 5 minutes, but not longer than about 100 hours depending on the alloy composition; cooling the alloy to a temperature above its order-disorder lattice transformation point, e.g., at about 600 C, so as to keep the alloy at the last mentioned temperature for a short while, e.g., 5 minutes to 1 hour, until uniform temperature is established throughout the alloy; and cooling the alloy from the temperature above the order-disorder lattice transformation point to room temperature at a rate faster than 1 C/hour but slower than 100 C/second, depending on the alloy composition.

With the present invention, it is also possible to produce the desired permeability and the high hardness by a process comprising steps of heating the alloy of the aforesaid composition in vacuo or in a non-oxidizing atmosphere, for the purpose of thorough solution treatment and homogenization, at 800 C or higher, preferably l,100 C or higher, for at least 1 minute, preferably longer than about 5 minutes, but not longer than about hours depending on the alloy composition; cooling the alloy to a temperature above its order-disorder lattice transformation point, e.g., at about 600 C. so as to keep the alloy at the last mentioned temperature for a short while, e.g., 5 minutes to 1 hour, until uniform temperature is established throughout the alloy; cooling the alloy from the temperature above the orderdisorder lattice transformation point to room temperature at a rate faster than 1 C/hour but slower than 100 C/second, depending on the alloy composition; reheating the alloy at a temperature below the order-disorder lattice transformation point for at least 1 minute, preferably longer than about 5 minutes, but not longer than 100 hours depending on the alloy composition; and cooling it to room temperature.

The aforesaid solution treatment should preferably be effected at a temperature above 1,100 C, especially about 1,250 C, instead of at a temperature of 800 C to 1,100 C, for an extended period of time, so as to effect the solid solution treatment as thoroughly as possible. The thorough solid solution treatment results in an outstanding improvement of the magnetic properties of the alloy.

The manner in which the alloy is cooled from the solution treatment temperature to a temperature above its order-disorder lattice transformation point, e.g., to about 600 C, does not affect its magnetic properties so seriously, regardless of whether it is cooled quickly or slowly. The cooling speed when the alloy temperature crosses its order-disorder lattice transformation point has profound effects on the magnetic properties of the alloy, and hence, it is necessary to cool the alloy from its order-disorder lattice transformation point of about 600 C at a rate faster than 1 C/hour but slower than 100 C/second. Such range of the-cooling speed is selected in order to cause the degree of order of the alloy to fall in a range of 0.1 to 0.6, preferably 0.2 to 0.5. If the alloy is comparatively quickly cooled at about 100 C/second, its degree of order becomes comparatively small, e.g., at about 0.1. Quick cooling faster than 100 C/second results in a degree of order smaller than 0.1 and does not provide the desired permeability.

On the other hand, excessively slow cooling, slower than 1 C/hour, tends to make the degree of order too large in excess of 0.6, so that the desired high permeability cannot be achieved.

The inventors have found-that the permeability of the alloy of the invention can be maximized when the degree of order of the alloy falls in a range of 0.1 to 0.6. The aforesaid cooling from a temperature above the order-disorder lattice transformation point of the alloy at a rate faster than 1 C/hour but slower than 100 C/second will results in the desired degree of order in the range of 0.1 to 0.6. The permeability of the alloy thus treated, especially when it is quickly cooled, may be further improved by tempering or reheating it to a temperature below its order-disorder lattice transformation point, e.g., in a range between 200C and 600C.

In short, with the above method, the permeability of the alloy of the aforesaid composition is maximized by making its degree of order be 0.1 to 0.6 by applying thorough solution treatment at 800 C or higher, preferably I,l C or higher, followed by cooling at a proper rate in the aforesaid range. When quick cooling fails to provide the high permeability, the additional tempering, preferably in the range of 200 C to 600 C, will improve its degree of order for raising its permeability.

Generally, a higher treating temperature tends to allow a shorter treating time, while a lower treating temperature tends to require a longer treating time. Similarly, a greater mass tends to require a longer treating time, while a smaller mass tends to allow a shorter treating time.

In cooling the alloy having the aforesaid composition, according to the present invention, from a temperature above its order-disorder lattice transformation point of about 600 C to a low temperature, e.g., to room temperature, the proper cooling speed for maximizing its permeability somewhat varies depending on its composition, but the cooling speed to be used in the method of the present invention is usually so slow that cooling in a furnace is preferred. With conventional nickel-iron alloys containing no tantalum, e.g., Permalloy, high permeability cannot be obtained unless it is quickly cooled, for instance by forced-air-cooling. The difference of the cooling speed between the conventional alloys a8d the alloy of the present invention is a very important factor in improving the properties of magnetic material.

For instance, after shaping magnetic recordingreproducing heads, such heads are usually heat treated for eliminating internal stress caused in the heads by the shaping process. To retain their proper shape and to avoid the oxidation of their surface, slow cooling in vacuo or in a non-oxidizing atmosphere is preferable. The conventional alloys requiring quick cooling for producing a high permeability is not suitable for such slow cooling. On the other hand, the alloy according to the present invention is particularly suitable for such post-shaping heat treatment.

BRIEF DESCRIPTION OF THE DRAWINGS For a better understanding of the invention, reference is made to the accompanying drawings, in which:

FIG. 1A is a graph illustrating the relation between the composition of nickel-iron-tantalum alloys and their initial permeability;

FIG. 1B is a graph illustrating the relation between the composition of nickel-iron-tantalum alloys and their maximum permeability;

FIG. 2A is a graph representing sections along the lines 11-0 of FIGS. 1A and 1B (Fe:Ta 08:1 for n 1.2:1 for u FIG. 2B is a graph representing sections along the lines b-b' of FIGS. 1A and 1B (NizTa 4.921 for n 5.6:1 for ;1.,,,);

FIG. 2C is a graph representing sections along the lines c-c' of FIGS. 1A and 1B (Ni:Fe 61:1 for p.,,, 6.9:] for ;1.,,,);

FIG. 3A is a graph showing the relation between the initial permeability of Specimen No. 35 of the alloy according to the present invention and their heating temperature and heating time;

FIG. 3B is a graph showing the relation between the maximum permeability of Specimen No. 20 of the alloy according to the present invention and their heating temperature and heating time;

FIGS. 4A and 4B are graphs showing the effects of different cooling speeds on the initial permeability and the maximum permeability of the alloys of the present invention, respectively;

FIG. 5 is a graph showing magnetic hysteresis curves of Specimens No. 20 and No. 35 of the alloy according to the present invention; and

FIG. 6 is a graph representing the effects of different tantalum contents in the alloy according to the present invention on their electric resistivity and Vickers hardness, assuming a constant nickel content of about 73 Wt. percent.

DESCRIPTION OF THE PREFERRED EMBODIMENT A method for making an alloy according to the present invention will now be described step by step.

In order to make the alloy of the present invention, a suitable amount of a starting material consisting of 60.2 to 85.0 Wt. percent of nickel, 6.0 to 30.0 Wt. percent of iron, and 3.l to 23.0 Wt. percent of tantalum is melted by a melting furnace in air, preferably in vacuo or in a non-oxidizing atmosphere; a small amount (less than 1 Wt. percent) of a de-oxidizer and a de-sulfurizer, e.g., manganese, silicon, aluminum, titanium, calcium alloy, and the like, is added in the melt for removing impurities as far as possible; and the molten metal thus prepared is thoroughly agitated to homogenize its composition.

For the purpose of testing, a number of different alloy specimens were prepared in the aforesaid manner. Each of the alloy specimens was poured into a mold for producing an ingot. The ingot was then shaped into sheets, each being 0.3 mm thick. The alloys can be shaped into any other suitable form by forgiving or rolling at room temperature or at an elevated temperature.

Rings with an outer diameter of 44 mm and an inner diameter of 36 mm were punched out of the sheets thus prepared. The rings were then heated at 800 or higher, preferably at l,l00 C or higher, for at least 1 minute, preferably longer than 5 minutes, but not longer than hours, in vacuo or in hydrogen or other nonoxidizing atmosphere, and then gradually cooled to a temperature close to their order-disorder transformation point of about 600 C (e.g., at a cooling speed of 1 C/second to 50 C/hour), so as to hold them at such temperature for a while (e.g., 5 minutes to 1 hour) until their composition become homogeneous, and finally they were further cooled at a suitable speed (e.g., l C/hour to 100 C/second, preferably 10 C/hour to 10 C/second, depending on the alloy composition). For certain alloy compositions, the specimens were further heated at a temperature below their order-disorder lat-. tice transformation point, e.g., at about 600 C, for at least 1 minute, preferably longer than 5 minutes, but not longer than 100 hours, and then cooled.

The permeability of the ring specimens thus heat treated was measured by a conventional ballistic galvanometer method. The highest values of the initial permeability (p and the maximum permeability (p of 8w 3 83: 8 8H 2 on: 9% 9m H 3 8o as 2 3m. w EN H o 8 H; Q56 2 2 $66 8; 822 23H 8m N m 3H; 9: 0 2 mm *5 8H SHHNH 3m m 33 92 2: 832 0 83 9H m 33 0 2 HYNH SN o i 2a a 2 2 E8 0 8 MN Q8 2: 8w an 2: m Haw NH O 2 0 NH mmdw MNHHZH 3% 85 2 83w 5 m on: 92 9Q NHN mi. 23 m3: SS6 o3 N 8;: 818 8H m .5 H 0 2 0 2 STE 828 8w Ham; HEH 9:

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SH 9% 22 NM 3 38d HE H.863 23H 3a m $2 0 m mH 2: in 2 2 28d 23 80 3 95 3 8m m 31H QHH 92 Q: wm 08 w E 2 $8 0 8m m 2: Su a HHH 8H. m SN H o 3 n HH :1: EH: 28 0 9% 822 2H 3 8w m on: o S n 3 @wH 9mm I 80 2: 32H 2 m on; 3: 3H HQ 8: 2% $85 and 8g. 8: am NH SN H HHdH HQH 2 3 $86 8: 83E 8%: 8w m on: H; 9 2 8H N 8 0% w H 8 58 o in H. 8H N8 96 3 8H m m c2 H HH HH 0 MH 9: 2% E; 8:2 EQMH Sm M 2 ow H3: 2 in 08 2 25 3 81w M H5; H3 92 $8 H 33 0 8m 3 0 83. H EH 2 6 5 H4 Q5 H 9 5 0 OH 2 Q0 DH 8 9H. PH Hz & 3 5 32 .5: bg mwmwh ow 2 3:5 359 $5555 2 5555C .33 E3. M Ego; 8585 $2: as 09 335 3Q 30v 8v 3% $253 $253 H8 0 25 as ll SHHQEQS the specimens proved to be 34,800 and 256,000, respectively. It was also found that the specimens had a considerably high hardness and a large electric resistivity.

FIG. IA shows contours of the highest values of the initial permeability n of the nickel-iron-tantalum alloys of different compositions which were obtained by the aforesaid various heat treatments. Similar contours for the highest values of the maximum permeability of the nickel-iron-tantalum alloys of different compositions are shown in FIG. 1B after applying the aforesaid variety of heat treatments.

FIGS. 2A, 2B, and 2C are schematic sections of FIGS. 1A and 1B, taken along the lines a-a, b-b and c-c, respectively, illustrating the highest values of the initial permeability u, and the maximum permeability u along such sections.

Table I shows the physical properties of selected alloy specimens.

It is apparent from FIGS. 1A to 2C that the addition of 3.1 to 23.0 Wt. percent of tantalum (Ta) into binary nickel-iron alloys greatly improves the magnetic properties of the alloys, and the heating of such ternary alloys at a temperature higher than 1,l C further improves the permeability of the ternary alloys. Thus, with the alloys of the present invention, extremely high initial permeability and maximum permeability can easily be obtained. For instance, Specimen No. 35 consisting of 73.0 Wt. percent of nickel, 12.0 Wt. percent of iron, and 15.0 Wt. percent of tantalum showed an initial permeability of 34,800, when it was heated at 1,250 C for 3 hours and cooled in a furnace to 600 C at 240 C/hour for keeping it at 600 C for minutes and then cooled to room temperature at a cooling.

speed of 400 C/hour. Another alloy, i.e., Specimen No. 20, consisting of 75.5 Wt. percent of nickel, nickeliron l3.5 Wt. percent ofiron, and l 1.0 Wt. percent of tantalum showed a maximum permeability of 256,000, when it was heated at 1,250 C for 3 hours and cooled in a furnace to 600 C for keeping it at 600 C for 10 minutes and then cooled to room temperature at a cooling rate of 240 C/hour. Such values of permeability are considerably larger than those obtainable by using conventional binary alloys containing no tantalum; namely, a conventional nickel-iron alloy consisting of 78.5 Wt. percent of nickel and 21.5 Wt. percent of iron shows an initial permeability of 8,000 and a maximum permeability of 100,000, when it is heated at l,050 C and slowly cooled to 600 C followed by quick cooling from 600 C.

FIG. 3A shows the effects of different high heating temperatures and the heating time at such temperatures on the initial permeability of the ternary alloy, for the case of Specimen No. 35 of Table 1. FIG. 3B shows similar effects on the maximum permeability of Specimen N0. 20. The values of the permeability in FIGS. 3A and 3B were determined after cooling Specimens No. 35 and No. 20 from the illustrated high temperature in the range of 1,050 C to 1,350" in a special manner; namely, it was cooled to 600 C in a furnace for keeping it at 600 C for 10 minutes and then cooled to room temperature at a speed of 400 C/hour in the case of the initial permeability of Specimen No. 35 and 240 C/hour in the case of the maximum permeability of Specimen No. 20. It is apparent from FIGS. 3A and 313 that the permeability is materially influenced by the high heating temperature and the duration in which the alloy is heated at such high temperature. Thus, there are an optimal heating temperature and an optimal heating time for each alloy composition, in order to S maximize the permeability. More particularly, a heat treatment at a temperature below l,l00 C results in comparatively low permeabilities; namely, an initial permeability not greater than 20,000 and a maximum permeability not greater than 150,000. On the other 10 hand, a high temperature heat treatment at l,100 C or higher results in comparatively high permeabilities; namely, an initial permeability greater than 20,000 and a maximum permeability greater than 150,000.

In order to test the effects of the cooling speed and reheating after the cooling from the aforesaid high temperature, a series of tests were carried out. The results are shown in FIGS. 4A and 4B. In the figures, curves A to D correspond to selected Specimens of Table l, as shown in Table 2.

Table 2 Composition Curve Specimen (Wt.%)

No. in Table 1 Nickel Iron Tantalum A 8 76.0 16.0 8.0 B 20 75.5 13.5 11.0 C 35 73.0 12.0 15.0 D 43 72.5 10.5 17.0

In the figures, non-primed symbols in FIGS. 4A and 4B (A,, A B,, B B,,, C,, C C,,, D,, and D represent the permeability of the corresponding alloys, which were treated by heating at l,250 C for 3 hours, cooling to 600 C at 240 C/hour, and then further cooled from 600 C to room temperature at different speeds as specified by such non-primed symbols in the figures. The

solid line curves A to D were drawn by connccting such non-primed points for the corresponding alloys.

Primed points in FIGS. 4A and 4B (A,, A 3,, B

B C,, C C D,', and D represent the permeability of the corresponding alloy Specimens after further treating them from the corresponding non-primed conditions, respectively. The heat treatments for the primed points were as follows.

A, AFter A,, Specimen No. 8 was reheated at 350 C for 1 hour and cooled in air.

A, After A Specimen No. 8 was reheated at 350 C for 30 minutes and cooled in air.

B, After 8,, Specimen No. 20 was reheated at 400 C for 1 hour and cooled in air.

B After 8,, Specimen No. 20 was reheated at 400 C for 30 minutes and cooled in air.

B After B Specimen No. 20 was reheated at 400 C for 1 hour and cooled in air.

C, After C,, Specimen No. 35 was reheated at 350 C for 30 minutes and cooled in air. C After C Specimen No. 35 was reheated at 400 C for 1 hour and cooled in air.

C After C Specimen No. 35 was reheated at 400 C for 1 hour and cooled in air. D, After D,, Specimen No. 43 was reheated at 400 C for 30 minutes and cooled in air. D After D Specimen No. 43 was reheated at 400 C for 1 hour and cooled in air. The following trends are noticed in FIGS. 4A and 48. For alloys with 8.0 Wt. percent of tantalum, quick cooling is necessary in order to obtain a high permeability, initial or maximum, and the reheating, e.g., at 350 for 1 hour, tends to reduce the permeability. As the tantalum content increases, e.g., toward 11.0 to 17.0 Wt. percent, high permeabilities can more frequently be obtained by slower cooling. In general, if the alloys are comparatively quickly cooled from 600 C the succeeding reheating tends to noticeably increase their permeability, while if the alloys are comparatively slowly cooled from 600 C the succeeding reheating tends to jeopardize their permeability. The aforesaid trends are noticed both in the initial permeability and the maximum permeability.

FIG. 5 illustrates the hysteresis curves for the alloy Specimens having the highest permeability, i.e., Specimens No. 35 and No. 20. It is apparent from the figure that the hysteresis loss of Specimens No. 35 and 20 is extremely small.

The present invention will now be described in further detail by referring to specific Examples, which are selected from the Specimens of Table l.

EXAMPLE 11 Alloy Specimen No. 8 consisting of 76.0 Wt. percent of nickel, 16.0 Wt. percent of iron, and 8.0 Wt. percent of tantalum, as listed in Table 1., was made by using 99.8 percent pure electrolytic nickel, 99.97 percent pure electrolytic iron, and 99.9 percent pure tantalum. An ingot of the Specimen was formed by melting 800 grams of the starting pure metals in vacuo by using a crucible disposed in a high-frequency electric induction furnace, agitating the molten metal so as to produce a homogeneous melt of the alloy, and pouring the melt into a metallic mold having a cylindrical hole of 25 mm diameter and 170 mm height. The ingot was hot forged at about 1,000 C into 7 mm thick sheets. The sheets were hot rolled at about 600 to 900 C to a thickness of 1 mm, and then cold rolled at room temperature to make them into thin sheets of 0.3 mm thickness. Rings with an inner diameter of 36 mm and an outer diameter of 44 mm were punched out from the thin sheets.

The rings thus formed were subjected to different heat treatments, as shown in Table 3. Physical properties of the rings after the treatments are also shown in Table 3.

' EXAMPLE 2 Alloy Specimen No. 20, consisting of 75.5 Wt. percent of nickel, 13.5 Wt. percent of iron, and 11.0 Wt. percent of tantalum, was made by using the same materials in a similar manner as Example 1, so as to make similar rings. Different heat treatments were applied to the rings of Specimen No. 20, as shown in Table 4, together with the physical properties of the rings thus treated.

EXAMPLE 3 Alloy Specimen No. 35, consisting of 73.0 Wt. percent of nickel, 12.0 Wt. percent of iron, and 15.0 Wt. percent of tantalum, was made by using the same material in a similar manner as Example 1, so as to make similar rings. Different heat treatments were applied to the rings of Specimen No. 35, as shown in Table 5, together with the physical properties of the rings thus treated.

Thus, with the method according to the present invention, the heat treatment may be completed only by a primary treatment, which consists of heating a ternary alloy with a composition falling in the specific range of the invention, in a non-oxidizing atmosphere or in vacuo at 800 C or higher, preferably above l,l00 C, for at least 1 minute, preferably longer than 5 minutes, but not longer than about 100 hours, depending on the alloy composition, gradually cooling the alloy to about 600 C (e.g., at about 1 C/second to 50 C/hour), holding at this temperature for a short while (5 minutes to 1 hour), and then cooling the alloy from about 600C to room temperature at a cooling speed of 1 C/hour to 100 C/second, preferably 10 C/hour to 10 C/second.

According to the present invention, it is also possible to apply a secondary heat treatment to the alloy treated by the aforesaid primary heat treatment, which secondary heat treatment comprises steps of heating the alloy in a non-oxidizing atmosphere or in vacuo at a temperature below the order-disorder lattice transformation point of the alloy, preferably at about 600 C, for at least 1 minute, preferably longer than 5 minutes, but not longer than about 100 hours, and then gradually cooling.

The optimal cooling speed to obtain excellent magnetic properties with conventional nickel-iron binary alloys is comparatively quick. In the case of nickeliron-tantalum ternary alloys, according to the present invention, the optimal cooling speed for obtaining excellent magnetic properties decreases as the tantalum content in the alloy increases. With the tantalum content of 15 Wt. percent and 1 l Wt. percent which gives the highest permeability among all the Specimens, the optimal cooling speed is so slow that it is preferable to cool it in a furnace. It is one of the important features of the present invention that the outstandingly high permeability of the alloy can be produced by a very simple heat treatment. 7

Conventional materials for magnetic recording and reproducing heads have a shortcoming in that the passage of magnetic tape in contact with such heads tends to abrade the heads, which head abrasion may cause deterioration of the quality of the signals, e.g., sound quality, recorded or reproduced by the head. Accordingly, the alloy for magnetic heads should preferably have a high hardness and a high abrasion resistivity. Conventional nickel-iron alloys for magnetic heads have a Vickers hardness in the order of about 130, which is not high enough for ensuring a high abrasion resistivity. On the other hand, the Vickers hardness of the alloy according to the present invention increases with the tantalum content, as shown in FIG. 6 and Table l, and a Vickers hardness as high as 150 to 246 can be obtained by adding 3.1 to 23.0 Wt percent of tantalum. The alloy having the highest permeability, which contains 15.0 Wt. percent of tanalum, shows a Vickers hardness of 210. Thus, the abrasion resistivity TABLE 3 Residual Hysteresis magnetic Coercive loss (erg per Saturated Initial Maximum flux denforce 0111. per flux density permepemiesity (G) (e) cycle) (G1 at mag- Electric \'ickers Item ability abill netic field resistivity hardness No. Heat treatment (,u At maximum flux density of 5.000 G of 000 Oe. tun-(111.1 (11v) I Heated at 1,150 C. in hydrogen for 3 11,600 112,800 4,410 0.0150 22.37 8, 910 45. 6 176 hours, cooled to 600 C. at 240 C./hour, and cooled to room temperature at 13,000 C./hour. 11 After I, reheated at 350 C. in vacuo for 1 0, 800 103,000

hour. III Heated at 1,250 C. in hydrogen for 3 13, 020 120,600 4,370 0. 0127 20.15 8,920 4-1. T 174 hours, cooled to 600 C. at 240 CJhour, and cooled to room temperature at 2,800 C./hour. 1V After III, reheated at 350 C. in vacuo for 10,500 101,500 .1

1 iour. Heated at 1,250 C. in hydrogen for 3 0, 280 108, 200

hours, cooled to 600 C. at 240 C./hour, and cooled to room temperature at 240 C./hour. VI After V, reheated at 350 C. in vacuo for 5, 000 73, 600

30 minutes. \Il..... Ileated at 1,250 C. in hydrogen for 0 13, 000 120,200 4, 350 0.0128 21. 04 8,930 45. 3 172 hours, cooled to 600 C. at 240 C./honr, and cooled to room temperature at 2,800" (1. our. lll. After VII, reheated at 350 (1. in vacuo for 7, 800 103,000

1 hour. lX.... lleated at 1,350 C. in hydrogen for 3 13, 080 121,010 4,300 0.0130 20. 08 8,020 44.0 172 hours, cooled to 600 C. at 240 ()Jhour, and cooled to room temperature at 8,000 C./hour. X After IX, reheated at 350 C. in vacuo for 11,750 110,300

1 hour.

TABLE 4 Residual Hysteresis magnetic Coercive loss (erg per Saturated Initial Maximum flux denforce cmfl per flux density permepermesity (G) (Oe.) cycle) (0) at mag- Electric Vickcrs Item ability ability netic field resistivity hardness No. Heat treatment 1,.) m) At maximum flux density of 5,000 G of 000 0c. o-cm.) (11v) I Heated at1,150 C. in hydrogen for3 hours, 14, 640 240, 000 4, 505 0.0110 10. 77 58. 8 190 cooled to 600 C. at 240 C./hour, and cooled to room temperature at 800 C/ hour. 11 After I, reheated at 400 C. in vacuo for 30 9, 410 217, 300

minutes. I11 Heated at1,250 C. in hydrogen for 3 hours, 14, 630 192, 200 4,490 0.0123 21.30 8, 240 53. 7 190 cooled to 600 C. at 240 C./hour, and cooled to room temperature at 2,800 C./hour. IV After III, reheated at 400 C. in V00110f01' 1, 000 216, 000

1 hour. IIcatcd at1,250 C. in hydrogen for 3 hours, 12, 070 256,000 4, 470 0.0110 52 8,250 59. 0 192 cooled to 600 C. at 240 C./hour, and cooled to room temperature at 240 C./hour. VI After V, reheated at 400 C. in vacuo for 10, 300 222, 500 4,450 0.0115 21. 24

minutes. VII. Heated at 1,250 C. in hydrogen for 9 hours, 18,000 253,000 4, 480 0.0107 20. 33 8, 230 57. 8 190 cooled to 600 C. at 240 C./hour, and cooled to room temperature at C./h011r. V111. After VII, reheated at 400 C. in vacuo f r 11, 000 23 hour. 1); Heated at1,350 C.inhydrogenfor3hours. 11,300 252,600 4. 515 0.0117 18.70 58.5 15

cooled to 600 C. at 240 C./hour, and cooled to room temperature at 400 C./hour. X After IX, reheated at 400 C. in V8000 101 J, 700 06, 500

1 hour.

79 Wt. percent of nickel and about 21 Wt. percent of iron is in the order of 16 ufl-cm. On the other hand, with the alloys according to the present invention, the electric resistivity comparatively rapidly increases with the tantalum content, as can be seen from FIG. 6 and Table l. The use of 3.1 to 23.0 Wt. percent of tantalum in the alloy of the present invention results in an elecpresent invention are as easily workable as conventional nickel-iron binary alloys; namely, the alloy of the invention can easily be forged, rolled, drawn, swaged, or punched.

The high hardness of the alloy according to the present invention makes the alloy particularly suitable for magnetic recording and reproducing heads, as pointed out in the foregoing. Furthermore, the outstandingly high permeability and the high electric resistivity of the alloy of the invention are also attractive in conventional electric and magnetic devices of various other types.

The contents of nickel, iron, and tantalum are restricted to 60.2 to 85.0 Wt. percent, 6.0 to 30.0 Wt. percent, and 3.1 to 23.0 Wt. percent, respectively, according to the present invention, because the alloy composition in the aforesaid range produces a high permeability and a high hardness suitable for magnetic TABLE Residual 11 ysteresls magnetic (loereive loss (erg per Saturated Initial Maximum flux den force em. per flux density permepermesity (G) (00.) cycle) (G) at mag- Electric Vickers 1m ability ability netie field resistivity hardness No. Heat treatment (#0) (I At maximum flux density of 5.000 G of 000 Oe. u-cm.) (11v) 1 lieated at 1,150 C. in hydrogen for 3 30,100 110,200 2,550 0.0137 18,68 74 3 31g lmurs,-eoelcd to 000 C. at 240 (L/hour, and cooled to room temperature at 400 (L/hour. l l After I, rebooted at 400 C. in vacuo for 1 26, 000 87,500

hour. 111 Heated at 1,250 C. in hydrogen for 3 34,800 '100, 200 2,530 0.0075 10.15 6, 080 74.0 210 hours, cooled to 600 C. at 240 C./hour, and cooled to room temperature at 400 C./hour. 1V After III, reheated at 400 C. in vacuo for 30,000 161, 000

1 our. V Heated at 1,250 O. in hydro en for 3 28,250 184,300 3,060 0.0142 24.05 6,960 73.5 208 hours, cooled to 600 C. at 240 C./hour, and cooled to room temperature at 240 C./hour. \I Alter V, reheated at 400 C. in vacuo for 24,800 150,500

1 hour. \'II Heated at 1,250 C. in hydrogen for 9 34, 700 199,500 3,150 0.0118 23.51 6,970 73.7 210 hours, cooled to 600 C. at 240 C./hour, and cooled to room temperature at 400 C./hour. \'III Ami-V11, reheated at 400 C. in vacuo for 25,700 163,000 2,870 0.0153 21, 42

2 ours. IX Heated at 1,350 C. in hydrogen for 3 34,000 201,000 3,080 0.0125 23.86 6, 980 73.5 207 hours, cooled to 600 C. at 240 CJhour, and cooled to room temperature at 100 C./h0ur. X Alter; IX, reheated at 400 C. in vacuo for 26, 600 153, 600

2 ours.

heads, but alloy compositions outside the aforesaid range result in too low values of permeability and hardncss to use the alloy for magnetic heads.

The suitable contents of the ingredients in the alloy according-to the present invention will now be deinitial permeability n, of 34,800 and a maximum permeability u of 256,000. With nickel content less than 60.2 Wt. percent, the initial permeability u, is reduced to levels below 3,000, despite that a comparatively high maximum permeability u, can be achieved. On the other hand, with nickel content in excess of 85.0 Wt. percent, the initial permeability u, and the maximum permeability a, become less than 3,000 and 10,000, respectively. Thus, the nickel content is restricted to 60.2 to 85.0 Wt. percent.

2. 6.0 to 30.0 Wt. percent of iron:

With the iron content of 6.0 to 30.0 Wt. percent, excellent magnetic properties can be obtained. On the other hand, with iron content of less than 6.0 Wt. percent or in excess of 30.0 Wt. percent, the initial permeability ,u.,, and the maximum permeability u,,, are always below 3,000 and 10,000, respectively. Thus, the iron content is restricted to 6.0 to 30.0 Wt. percent.

3. 3.1 to 23.0 Wt. percent of tantalum: 7 With the tantalum content in the aforesaid range, ex-

300 Wt. percent of iron, 3.1 to 23.0 Wt; percent of tantalum and an inevitable amount of impurities. An ingot of the alloy of the invention may be made by pouring a melt of the alloy into a suitable mold. The ingot may be shaped into a desired form by working it at room temperature or at an elevated temperature, for instance by forging, rolling, drawing, swaging, or the like.

After the shaping, the alloy is heat treated by heating it at 800 C or higher (preferably higher than l,l00 C) in a non-oxidizing atmosphere, e.g., hydrogen, or in vacuo for at least I minute, preferably longer than 5 minutes, but not longer than about I00 hours, gradually cooling to a temperature above its order-disorder 0 transformation point, e.g., to about 600 C (for inccllent magnetic properties and high hardness can be 23.0 Wt. percent, the initial permeability n, and the maximum permeability u become smaller than 3,000 and 10,000, respectively. The excessively high tantalum content also results in the deterioration of the workability of the alloy, especially its forgeability and rollability. Thus, the tantalum content is restricted to 3.1 to 23.0 Wt. percent.

In short, the alloy according to the present invention' consists of 60.2 to .0 Wt. percent of nickel, 6.0 to

stance, at l" C/second to 50 C/hour), keeping it at such temperature for a short while (e.g., 5 minutes to 1 hour) until uniform temperature distribution is achieved throughout the alloy, and then cooling it to room temperature at a cooling speed of from 1 C/hour to C/second, preferably 10 C/hour to 10 C/second, depending on the alloy composition. For certain alloy compositions, the alloy may be reheated to a temperature below its order-disorder lattice transformation point, e.g., below about 600 C, for at least 1 minute, preferably longer than 5 minutes, but not longer than about 100 hours. With such heat treatment, high permeability including an initial permeability u, of 34,800 and a maximum permeability of 256,000 can be obtained. In addition to the high permeability, the alloy according to the present invention has a number of properties suitable for magnetic recording and reproducing heads; namely, a comparatively high electric resistivity, a high hardness, and a high workability at room temperature and at an elevated temperature in terms of forgeability, rollability, drawability, and swageability.

With the alloy of the present invention, extremely high values of initial and maximum permeability can be generated by using the following composition and applying any of the following heat treatments to the alloy.

al. An alloy consisting of 60.2 to 85.0 Wt. percent of nickel, 6.0 to 30.0 Wt. percent of iron, 3.1 to 23.0

Wt. percent of tantalum, and an inevitable amount of impurities is heated at a temperature above 800 C, preferably above 1,100 C, in a non-oxidizing atmosphere or in vacuo for at least 1 minute but not longer than about 100 hours, gradually cooled to an intermediary temperature slightly above the order-disorder lattice transformation point of the alloy, for instance to about 600 C, and cooled to room temperature from the intermediary temperature at a cooling rate in a range of 1 C/hour to 100 C/second, preferably 10 C/hour to 10 C/second. Whereby, one can obtain an initial permeability of about 3,000 to 34,800 and a maximum permeability of about 10,000 to 256,000.

a2. After the cooling to room temperature, the alloy of the preceding item (a1) may be reheated at a temperature below its order-disorder lattice transformation point, e.g., below about 600 C, in a nonoxidizing atmosphere or in vacuo for at least 1 minute, preferably longer than 5 minutes, but not longer than about 100 hours, so as to generate the permeabilities of the item (a1).

bl. An alloy consisting of 69.5 to 77.8 Wt. percent of nickel, 8.5 to 19.5 Wt. percent of iron, 3.1 to 20.2 Wt. percent of tantalum, and an inevitable amount of impurities is heated at a temperature above 800 C, preferably above 1,100 C, in a non-oxidizing atmosphere or in vacuo for at least 1 minute, preferably longer than 5 minutes, but not longer than about 100 hours, gradually cooled to an intermediary temperature slightly above the order-disorder lattice transformation point of the alloy, for instance to about 600 C, and cooled to room temperature from the intermediary temperature at a cooling rate in a range of 1 C/hour to 100 C/second, preferably C/hour to 10 C/second. whereby, one can obtain an initial permeability of about 10,000 to 34,800 and a maximum permeability of about 50,000 to 256,000.

b2. After the cooling to room temperature, the alloy of the preceding item (1) may be reheated at a temperature below its order-disorder lattice transformation point, e.g., below about 600 C, in a nonoxidizing atmosphere or in vacuo for at least 1 minute, preferably longer than 5 minutes, but not longer than about 100 hours, so as to generate the permeabilities of the item (b1):

01. An alloy consisting of 71.8 to 76.0 Wt. percent of nickel, 10.8 to 15.4 Wt. percent of iron, 9.0 to 16.5 Wt. percent of tantalum, and an inevitable amount of impurities is heated at a temperature above 800 C, preferably above l,100 C, in a non-oxidizing atmosphere or in vacuo for at least 1 minute, preferably longer than 5 minutes, but not longer than about 100 hours, gradually cooled to an intermediary temperature slightly above the order-disorder lattice transformation point of the alloy, for instance to about 600 C, and cooled to room temperature from the intermediary temperature at a cooling rate in a range of 1 C/hour to 100 C/second, preferably 10 C/hour to 10 C/ second.

whereby, one can obtain an initial permeability of about 10,000 to 34,800 and a maximum permeability of about 100,000 to 256,000.

02. After the cooling to room temperature, the alloy of the preceding item (c1) may be reheated at a temperature below its order-disorder lattice transformation point, e.g., below about 600 C, in a nonoxidizing atmosphere or in vacuo for at least 1 minute, preferably longer than 5 minutes, but not longer than about hours, so as to generate the permeabilities of the item (c1).

d1. An alloy consisting of 72.5 to 75.8 Wt. percent of nickel, 11.3 to 14.6 Wt. percent of iron, 9.8 to 15.6 Wt. percent of tantalum, and an inevitable amount of impurities is heated at a temperature above 800 C, preferably above 1,100 C, in a non-oxidizing atmosphere or in vacuo for at least 1 minute, preferably longer than 5 minutes, but not longer than about 100 hours, gradually cooled to an intermediary temperature slightly above the order-disorder lattice transformation point of the alloy, for instance to about 600 C, and cooled to room temperature from the intermediary temperature at a cooling rate in a range of 1 C/hour to 100 C/second, preferably 10 C/hour to 10 C/second. Whereby, one can obtain an initial permeability of about 10,000 to 34,800 and a maximum permeability of about 200,000 to 256,000.

d2. After the cooling to room temperature, the alloy fo the preceding item (d1) may be reheated at a temperature below its order-disorder lattice transformation point, e.g., below about 600 C, in a nonoxidizing atmosphere or in vacuo for at least 1 minute, preferably longer than 5 minutes, but not longer than about 100 hours, so as to generate the permeabilities of the item (d1).

What is claimed is:

l. A heat-treated alloy for magnetic recording and reproducing heads, consisting essentially of 60.2 to 85.0 Wt. percent of nickel, 6.0 to 30.0 Wt. percent of iron, and 3.1 to 23.0 Wt. percent of tantalum, said alloy having a degree of order of 0.1 to 0.6, an electric resistivity of 23 to 94 all-cm and a Vickers hardness of greater than and having high initial permeability and maximum permeability of above 3,000 and 10,000, respectively.

2. An alloy according to claim 1, wherein the nickel content is 69.5 to 77.8 Wt. percent, the iron content is 8.5 to 19.5 Wt. percent, and the tantalum content is 3.1 to 20.2 Wt. percent.

3. An alloy according to claim 1, wherein the nickel content is 71.8 to 76.0 Wt. percent, the iron content is 10.8 to 15.4 Wt. percent, and the tantalum content is 9.0 to 16.5 Wt. percent.

4. An alloy according to claim 1, wherein the nickel content is 72.5 to 75.8 Wt. percent, the iron content is 11.3 to 14.6 Wt. percent, and the tantalum content is 9.8 to 15.6 Wt. percent. 

2. An alloy according to claim 1, wherein the nickel content is 69.5 to 77.8 Wt. percent, the iron content is 8.5 to 19.5 Wt. percent, and the tantalum content is 3.1 to 20.2 Wt. percent.
 3. An alloy according to claim 1, wherein the nickel content is 71.8 to 76.0 Wt. percent, the iron content is 10.8 to 15.4 Wt. percent, and the tantalum content is 9.0 to 16.5 Wt. percent.
 4. An alloy according to claim 1, wherein the nickel content is 72.5 to 75.8 Wt. percent, the iron content is 11.3 to 14.6 Wt. percent, and the tantalum content is 9.8 to 15.6 Wt. percent. 